Apr 11 Protein Metabolism Made Easy To Understand

Let’s take a few minutes to talk about protein metabolism and how it works. This post is designed for people with little-to-no science background to help simplify how protein metabolism works in our body. I’m going to intentionally glaze over some of the more detail oriented aspects and focus on the larger picture.

Proteins in your body do a lot of things, including make your muscles go. They are composed of basic units called amino acids. There are 20 amino acids in total, and just like the alphabet, if you put those amino acids in different orders, your body makes different proteins. There are proteins that are specific to every organ in your body. Protein intake is essential and there are many dietary sources of protein. You may also hear another term polypeptide. This is just a fancy word for a chain of amino acids linked together and as far as we are concerned just means protein.

How does your body metabolize protein?

Protein metabolism consists of breaking down proteins you ingest or protein your body doesn't need into amino acids and then putting them back together in a different order for a new protein. Protein breakdown is called proteolysis and is a catabolic process; protein synthesis is an anabolic process. In general, the process of skeletal muscle metabolism is moderated by the two hormones insulin and glucagon. Ingested protein is partially broken down and absorbed in the small intestine where it travels to the liver. Here it is used to make many proteins. Skeletal muscle protein synthesis and repair actually occurs locally at the muscle. This is generally true for other organ systems as well.

How does exercise affect muscle protein? What is hypertrophy?

Previously, I have created a video that looks at what we know about muscle protein metabolism during exercise. I would encourage you to check that out for more specific information about what occurs while you are actively exercising.

Generally speaking, when you workout or exercise, your muscles are damaged with micro tears. In order to rebuild, get bigger and stronger, to hypertrophy, your muscles need protein. They are essential whether you are trying to lose weight, maintain where you are or gain strength. Any exercise routine is dependent on a good protein intake. As a rule of thumb for working out, eating your body weight (lbs) in protein grams per day should provide sufficient protein for muscle growth and I’ll discuss that more at the end.

Let's quickly define hypertrophy. Technically, hypertrophy is an increase in volume of organ or cell due to enlargement of cellular components. From a biologic and medical point of view, what we’re talking about is an increase in the size of the the individual cell. Hypertrophy can and does occur all over the human body, not just in muscles. When most people talk about hypertrophy, they are referring to an increase in skeletal muscle mass. This is essentially a summation of the cellular hypertrophy over millions of muscle cells. All of the cells get bigger so the muscle physically appears bigger as a result. If you have heard the term ‘atrophy’, this is literally the opposite, where the cells, aka skeleltal muscle fibers, shrink.

What happens if I increase my protein intake?

In general, there aren’t any negative consequence to eating too much protein. From a fitness, exercise and weight lifting point of view, you’ll really be challenging yourself to eat too much protein. Your body is so protein dependent that it can almost always find a place to use it. Your body has sophisticated mechanisms of utilizing it and getting rid of it in your urine if it needs to.

The one caveat here is if you have kidney problems because your body is unable to filter out the protein properly and can cause your body to start retaining excess fluid. So if you have problems with your kidneys, please talk to your doctor before you start increasing your protein or dramatically changing your diet. It’s worth noting that one study did find signs of amino acid toxicity in people consuming more than 2.2 grams of protein per lb per day. You don’t need to worry about this unless you’re eating more than double your bodyweight in grams of protein each day.

What happens to protein metabolism if I decrease my total calories or carbohydrate intake?

When you start dieting, either by decreasing calories or decreasing carbs or both, in general your blood sugar will go down as a consequence. Your body will try to raise your blood sugar by several mechanisms. One of these is breaking down your muscle proteins back into those amino acids. These products can then be converted to sugar. Your body specifically targets muscle protein when you’re fasting or dieting because compared to most other organs its expendable. Would you rather your body break down protein in your skeletal muscle or in your brain or your heart? Hopefully you said skeletal muscle because that is your body being smart about where it takes its protein from. After you have depleted your glycogen stores and have had no oral intake for at least 12-24 hours, your body begins to mobilize more stored fat (compared to protein). This is called ketogenesis and is another lecture for another day.

How can I prevent my body from breaking down my skeletal muscle protein?

So how do you prevent or at least minimize the amount of muscle breakdown during dieting? You increase your protein intake. This is important to mitigate more damage to skeletal muscle. It provides your body excess amino acids to rebuild the muscle that you may have worked out. It also provides excess amino acids that can be turned into glucose without targeting your muscle protein. That’s why most diets include a lot of protein, even for people who aren’t approaching it from a fitness perspective. This excess protein will blunt or minimize the effects of protein breakdown while you are dieting.

Recommendations

How much protein you should consume depends on your level of activity, your diet and your goals. The information below is quoted from a great article from examine.com on the subject. These recommendations are for individuals trying to gain and build muscle, trying to maintain muscle and also trying to lose weight.

If you are an athlete or highly active person currently attempting to lose body fat while preserving lean muscle mass, a daily intake of 1.5-2.2g/kg bodyweight (0.68-1g/lb bodyweight) would be a good target.

If you are an athlete or highly active person, or you are attempting to lose body fat while preserving lean mass, then a daily intake of 1.0-1.5g/kg bodyweight (0.45-0.68g/lb bodyweight) would be a good target.

If you are sedentary and not looking to change body composition much, a daily target of 0.8g/kg bodyweight (0.36g/lb bodyweight) and upwards would be a good target.

You might also be wondering what percentage of your diet should be protein based. The 2010 American Dietary Guidelines recommends an adult diet consist of 45-65% carbohydrates, 10-35% protein and 20-35% fat. I’m going to suggest that you deviate from that recommendation and don’t let your carbs be any more than 40% of your total daily caloric intake; protein and fats will make up the other 60%. Scale your protein intake up based on the recommendations above.

There are lots of great sources of protein. A quick list includes turkey and chicken breast, fish, cheese, pork, lean beef and veal, tofu, soy, eggs, yogurt and milk, nuts and seeds. Powdered protein (whey, soy, etc) is also a great supplemental source of protein.